1. Field of the Invention
This invention relates to a novel aroyl ketone derivative possessing UV-ray absorbing ability and outstanding stability against light, and to a UV-ray absorber and a cosmetic composition both containing such an aroyl ketone derivative and exhibiting a superior effect of protecting the skin from sunburn.
2. Description of the Background Art
Ultraviolet rays are known to cause various changes to the skin. In dermatology, UV-rays are classified into (a) long wavelength UV-rays of 400-320 nm, (b) medium wavelength UV-rays of 320-290 nm, and (c) short wavelength UV-rays of less than 290 nm. These are called UV-A, UV-B, and UV-C, respectively. The UV-rays contained in the sunlight are UV-A and UV-B, whereas UV-C is absorbed in the ozone layer and therefore scarcely reaches the ground.
The UV-B, when irradiated onto the skin in an amount exceeding a certain level, causes red spots or blisters on the skin. In addition, the UV-B tends to promote the formation of melanin, resulting in the melanoses or other adverse changes of the skin. On the other hand, UV-A induces melanism on the skin immediately after irradiation (instantaneous melanism). In addition, UV-A energy reaches the corium and brings about chronic changes in the blood vessel walls and the elastic fibers in connective tissues. Such behaviors of both UV-A and UV-B are considered to accelerate aging of the skin and to be a cause of wrinkles, spots or freckles.
As such effects of UV-rays on human skin have been clarified, various chemical compounds capable of absorbing UV-A and/or UV-B have been developed. Such UV-ray absorbers are desired to satisfy the following requirements (1) through (5):
(1) absorbing UV-A or UV-B light to the maximum.
(2) having good stability against heat and light.
(3) being free from toxicity, irritation, and any other harmful actions to the skin.
(4) having a long-lasting effect.
(5) having an excellent compatibility with cosmetic base materials.
Conventionally, for example, dibenzoylmethane derivatives are used as a UV-A absorber; and derivatives of cinnamate, benzophenone, p-aminobenzoic acid, salicylic acid, and the like are used as a UV-B absorber.
However, these conventional UV-ray absorbers can not necessarily satisfy the above requirements. Specifically, these UV-ray absorbers are known to be inadequate in the stability against light and to decompose or react by UV-ray irradiation (Int. J. Cosmetic Science, 10, 53, 1988). Such decomposition of UV-ray absorbers substantially decreases the lasting effect of compositions. Adverse effects to the skin resulting from decomposed substances themselves or compounds produced by the reaction of the decomposed substances and other components can not be neglected (Fragrance Journal, 84, 34, 1987).
Development of improved UV-ray absorbers which satisfy the above characteristics, especially UV-ray absorbers having excellent stability against light, has therefore been desired.
The inventors have synthesized many diketone derivatives and examined their characteristics, and, as a result, found that an aroyl ketone derivative represented by formula (I) shown below had an outstanding UV-A and UV-B absorbing ability and excellent stability against light, and further found that a cosmetic composition comprising the aroyl ketone derivative could efficiently protect the skin from being sunburnt.